gimp

Years ago for the NCCP website, I needed to generate charts that would appear as vector graphics (in PDF files) and as raster graphics (in PNG's).

The best solution at the time -- it may not be so any more -- was to write my own library of graph-drawing functions that generated SVG files, then run the GIMP in batch mode to convert those images to PNG files. (I know... I had a lot of time on my hands.)